Features/location of the pelvis (basin)
- 1. lower and smaller portion of the trunk
- 2. superiorly it is continuous with the abdomen
- 3. inferiorly it is separated from the perineum by the pelvic diaphragm (sheet of muscles)
Functions of pelvis
- 1. Acts to transmit upper body weight to the lower limbs and provides a stable base for lower limb function
- 2. Supports and protects the pelvic viscera
- 3. Forms part of the birth canal during delivery
What is the bony pelvis?
A ring of bone formed by the two hip bones (os coxae) anteriorly and laterally, and the sacrum and coccyx posteriorly.
What are the 3 parts of the hip bone?
- 1. ilium
- 2. ischium
- 3. pubis
Where do the 3 parts of the hip bone fuse?
At what age do the 3 parts of the hip bone fuse?
Features of the sacral canal
- -formed by the sacral vertebral foramina and is a downward continuation of the vertebral canal
- -has 4 pairs of intervertebral foramina that are continuous with the pelvic and dorsal sacral foramina
What does the sacral canal contain?
- 1. cauda equina
- 2. filum terminale
- 3. meninges
Where does the subarachnoid space end?
At the level of S2 vertebra
What passes through the sacral hiatus?
- 1. filum terminale
- 2. S5 nerves
Which side of the sacrum is concave and which is convex?
pelvic surface is concave, dorsal surface is convex
Where are the ventral rami of S1-4 transmitted, and where are the dorsal rami of S1-4 transmitted?
- ventral rami- through the 4 pairs of pelvic sacral foramina on the pelvic surface of the sacrum.
- dorsal rami- throught the 4 pairs of dorsal sacral faramina on the dorsal surface of the sacrum.
How many fused vertebral segments does the coccyx have?
Which direction do the paired coccygeal cornua project?
Which direction do the paired transverse processes of the coccyx project?
Description/location of pelvic inlet
- -plane bounded by the pelvic brim (linea terminalis)
- -extends along:
- 1. promontory and ala of sacrum
- 2. arcuate line of the ilium
- 3. pecten pubis
- 4. pubic crest
- 5. upper border of symphysis pubis
The pelvic inlet divides the pelvis into what two parts?
greater pelvis (pelvis major or false pelvis) and lesser pelvis (pelvis minor or true pelvis)
Where is the greater pelvis located?
above the pelvic inlet between the iliac bone. It is part of the abdominal cavity.
Where is the lesser pelvis located?
below the pelvic inlet. It forms the pelvic cavity, or simply the pelvis.
Description/location of pelvic outlet
- -diamond-shaped area extending from the symphysis pubis anteriorly to the coccyx posteriorly
- -bound on each side by:
- 1. ischiopubic ramus
- 2. ischial tuberosity
- 3. sacrotuberous ligament (ischial tuberosity -> sacrum)
Maximum diameters of inlet and outlet in the female and significance to childbirth
- inlet- transverse diameter 13.5 cm
- outlet- A-P diameter 11 cm
- -fetal head turns 90 degrees during delivery. It faces to the side as it passes through the inlet and faces posteriorly through the outlet.
Neutral position of the pelvis
ASIS and upper end of symphysis pubis are in same vertical plane
Functions of the pelvic floor
- 1. support the pelvic organs and their contents (ex: bowel, bladder, uterus)
- 2. withstand any increases in pressure in the abdominopelvic cavity
- 3. provide sphincter control of the perineal openings (urethra, vagina, anus)
General description of the perineum
-diamond shaped area between the thighs that contains the external genitalia and the anal region
In the perineum, two triangles are formed by a line drawn between what landmarks?
the ischial tuberosities
What two triangles make up the perineum?
urogenital triangle + anal triangle
What separates the perineum from the pelvic cavity?
the pelvic diaphragm (levator ani and coccygeus muscles)
What does the urogenital triangle of the perineum contain? Where is it positioned in the perineum?
external urogenital organs, positioned anteriorly
What does the anal triangle of the perineum contain? Where is it positioned in the perineum?
end of the anal canal and anus, positioned posteriorly
Innervates anus and external anal sphincter
inferior rectal branch of pudendal nerve (S2,3,4)
What is the ischioanal fossa? What structures are found here?
- -a large wedge-shaped space on each side of the anus filled with fat.
- -Pudendal VAN
External genitalia of the female
- 1. Mons pubis
- 2. Labia majora
- 3. Labia minora (forms the prepuce and frenulum of the clitoris)
- 4. Vestibule (contains openings of the urethra and vagina)
- 5. Bulbs of the vestibule (erectile tissue lying on each sideof the vaginal opening)
- 6. Clitoris (erectile tissue consisting of 2 crura and a body ending in the glans)
- 7. Greater vestibular (Bartholin's) glands (secrete mucus for vaginal lubrication)
External genitalia of the male
- 1. Penis, consisting of 3 cylinders of erectile tissue:
- a) paired dorsal corpora cavernosa, each attached along the ischiopubic ramus by its crus
- b) unpaired ventral corpus spongiosum containing the urethra and ending in the enlarged glans. The bulb is attached to the perineal membrane.
- 2. Scrotum-a fibromuscular sac of skin containing the testes and lower parts of the spermatic cords.
- Dartos muscle- layer of smooth muscle that wrinkles the skin of the scrotum.
The perineal branch of the pudendal nerve (S2,3,4) (that innervates the bulbospongiosus and ischiocavernosus) contains what fibers?
- somatic motor
- somatic sensory
Features of pelvic diaphragm
- -funnel-shaped musculofibrous sheet that closes off the pelvic outlet and forms the floor of the pelvic cavity
- -consists of 2 pairs of muscles: levator ani and coccygeus